On Fri, Mar 26, 2021 at 01:05:26PM +0100, Christoph Hellwig wrote:

On Fri, Mar 26, 2021 at 12:03:03PM +0000, Robin Murphy wrote:

quoted

This might happen to work out, but is far from correct. Just wait until you 
try it on a platform where the USB controller is behind an IOMMU...

It looks like something is more fundamentally wrong here - the device 
passed to DMA API calls must be the actual hardware device performing the 
DMA, which in USB-land I believe means the controller's sysdev.

The shiny new usb_intf_get_dma_device API provides the device to use.

Thanks Robin and Christoph for the feedback.

If I understand correctly, usb_intf_get_dma_device API is mainly for usb
host drivers? I just found usb_gadget_map_request_by_dev API: does it
make sense to replace usb_gadget_map_request with
usb_gadget_map_request_by_dev so we can pass the actual DMA-capable
hardware device (aspeed-vhub platform device) to the API?


Cheers,

Tao